Ink-jet printing mechanisms use printer pens that shoot droplets of ink onto a print medium to generate an image. Such mechanisms may be used in a wide variety of applications, including computer printers, plotters, copiers, and facsimile machines. An ink-jet printer typically includes a print-head having a plurality of independently addressable firing units. Each firing unit includes an ink chamber connected to an ink source, which may be a common ink source, and to an ink outlet nozzle. A transducer within the chamber provides the impetus for expelling ink droplets through the nozzles. In thermal ink-jet printers, the transducers are thin-film firing resistors that generate sufficient heat during application of a brief voltage pulse to vaporize a quantity of ink. This vaporization is then sufficient to expel a liquid droplet. It is useful to increase the efficiency of an ink-jet printer that uses a printer pen.